There is an ultrasonic joining method for joining materials to be joined together by ultrasonic vibration in a horizontal direction while applying pressure to a joining surface between the materials to be joined (see, for example, Patent Document 1). In the ultrasonic joining method described in Patent Document 1, there are a plurality of sets of materials to be joined, and the plurality of sets of materials to be joined can be joined together collectively, and at this time, a variation occurring in a joining state for each set of the materials to be joined due to generating a difference in the distance from the center of a horn to each welding point for each set of the materials to be joined can be prevented.
When a plurality of materials to be joined are collectively joined, if the energy generated by the vibration in each set of the materials to be joined is different, a variation occurs in the joining state of the materials to be joined, and a variation occurs in quality of a joint of each set of the materials to be joined. Therefore, in the ultrasonic joining method described in Patent Document 1, each of distances from a center point of an arc-shaped ultrasonic horn to joining points is made equal by disposing the joining points around the horn. This enables to avoid a variation occurring in the magnitude of vibration at each of the joining points during the vibration of the ultrasonic horn, and not to generate any difference in the joining state of each joint.
Patent Document 1: Japanese Unexamined Patent Application Publication No. H10-175083